Generating an Empty data.table with Column Names in R (2 Examples)
In this article, I’ll illustrate how to generate a blank data.table in the R programming language.
Setting up the Examples
We install and load the data.table package. For general information about the package data.table, we recommend you to take a look at this page.
install.packages("data.table") # Install & load data.table package
library("data.table")
For Example 2, we use the iris dataset. We therefore load the data and convert it to a data.table.
data(iris) # Load iris data set iris_DT_1 <- data.table::copy(iris) # Replicate the iris data set iris_DT_1 <- setDT(iris_DT_1) # Convert to data.table
head(iris_DT_1) # Printing the data head # Sepal.Length Sepal.Width Petal.Length Petal.Width Species # 1: 5.1 3.5 1.4 0.2 setosa # 2: 4.9 3.0 1.4 0.2 setosa # 3: 4.7 3.2 1.3 0.2 setosa # 4: 4.6 3.1 1.5 0.2 setosa # 5: 5.0 3.6 1.4 0.2 setosa # 6: 5.4 3.9 1.7 0.4 setosa
Example 1: Generate empty data.table
Let's create a data.table from scratch. We only select the names and types of the columns and create it with data.table() as shown below.
empty_DT <- data.table("A" = character(), # Generating an empty data.table
"B" = logical(),
"C" = double(),
"D" = factor())
str(empty_DT) # See the structure of the data
# Classes ‘data.table’ and 'data.frame': 0 obs. of 4 variables:
# $ A: chr
# $ B: logi
# $ C: num
# $ D: Factor w/ 0 levels:
# - attr(*, ".internal.selfref")=
empty_DT # Printing the data
# Empty data.table (0 rows and 4 cols): A,B,C,D
You see that there are zero rows in the data. For information about the different column types available in R, take a look at the description here.
Example 2: Set all values in a data.table to NA
Alternatively to generating a data.table from scratch, we can also take a data.table and set all its input values equal to NA. Below, we set all values in the iris data to NA.
iris_DT_2 <- data.table::copy(iris_DF_1) # Replicate the iris data set iris_DT_2[ !is.na(iris_DT_2) ] <- NA # Set all values to NA
str(iris_DT_2) # See the structure of the data # 'data.frame': 150 obs. of 5 variables: # $ Sepal.Length: num NA NA NA NA NA NA NA NA NA NA ... # $ Sepal.Width : num NA NA NA NA NA NA NA NA NA NA ... # $ Petal.Length: num NA NA NA NA NA NA NA NA NA NA ... # $ Petal.Width : num NA NA NA NA NA NA NA NA NA NA ... # $ Species : Factor w/ 3 levels "setosa","versicolor",..: NA NA NA NA NA NA NA NA NA NA ...
head(iris_DT_2) # Printing the data head # Sepal.Length Sepal.Width Petal.Length Petal.Width Species # 1 NA NA NA NA# 2 NA NA NA NA # 3 NA NA NA NA # 4 NA NA NA NA # 5 NA NA NA NA # 6 NA NA NA NA
Further Resources
Please find some related R programming language tutorials on topics such as merging, matrices, and variables in the following list:
- Merge Rows of Data Frames with Unequal Column Names
- How to Create an Empty Matrix in R
- Merge data.tables with Different Column Names in R
- Transpose Data Matrix & Maintain First Variable as Column Names
Note: This article was created in collaboration with Anna-Lena Wölwer. Anna-Lena is a researcher and programmer who creates tutorials on statistical methodology as well as on the R programming language. You may find more info about Anna-Lena and her other articles on her profile page.